The manufacture and setting of lime is chemically defined as
three separate processes:

Burning or calcining of calcium carbonate
by which carbon dioxide gas is driven off at temperatures
of about 800 degrees centigrade to produce lumplime or calcium
oxide.

Slaking or hydration of calcium hydroxide
by exothermic reaction with water to produce lime putty or
calcium hydroxide.

Setting or carbonation of calcium hydroxide
by slow reaction with carbon dioxide in the air to produce
calcium carbonate. This series of reactions is called the
lime cycle because this cycle of burning, slaking and carbonation
starts and ends with calcium carbonate.

The chemistry of hydraulic lime is more complicated. Along
with the lime cycle processes described above, complex reactive
clay minerals are formed during the burning process which when
wetted in the presence of calcium hydroxide react to form a
harder setting material.